Device for ventilating the middle ear

ABSTRACT

The invention relates to a device for ventilating the middle ear by means of a ventilation tube which is made of a tissue-compatible material, preferably titanium, and with a through-channel for air communication between the cavity of the middle ear and the outside air. The ventilation tube comprises, on the one hand, a front portion ( 2 ) which is arranged to be introduced into bone tissue and is designed so that a permanent anchoring is obtained in the bone tissue, and, on the other hand, a rear portion ( 6 ) which forms a passage through the skin. The ventilation tube further comprises an outer tube ( 1 ) which is made of the said tissue-compatible material and an inner tube ( 8 ) which is arranged releasably in the outer tube and whose inner bore forms the said through-channel ( 14 ) for air communication between the cavity of the middle ear and the outside air.

This application is a 371 of PCT/SE97/01447 field Sep. 12, 1997, andpublished as WO99/13811.

The present invention relates to a device for ventilating the middle earby means of a ventilation tube which is made of a tissue-compatiblematerial, preferably titanium, and which has a through-channel for aircommunication between the cavity of the middle ear and the outside air.

As is known, the function of the middle ear is to transmit sound energyfrom the environment to the inner ear, where the sound signals undergocomplex processes of interpretation. This transmission of sound energyfrom the environment to the inner ear requires an impedance conversionof the sound signal, since the sound energy is being conveyed from onemedium (air) to another medium (liquid) which is located in the innerear and which has a considerably higher impedance than air. With the aidof the auditory ossicles and the shape of the surrounding organs, animpedance conversion takes place in the middle ear. A basic condition ifnormal hearing is to be maintained is that the normal impedance in themiddle ear is retained and that the movement in the transmission chainis not damped, which necessitates a normally ventilated middle ear.

One of the commonest complaints seen in otology is, however,accumulation of liquid in the middle ear, which results in diminishedhearing. This is especially common among children but also occurs inadults with chronic inflammation of the middle ear. Puncturing thetympanic membrane and fitting a ventilation tube is therefore a commonoperation. In the USA alone, approximately one million operations ofthis type are performed each year. In total, some 5 million ventilationtubes are used each year for these operations in Western Europe, the USAand Japan, most of these being performed on children under anaesthesia.

Some of these children with middle ear problems do not improve as theygrow older, and instead the problems remain and become chronic in theadult years. The result is that the function of the middle ear isgradually destroyed. In most cases there is a progressive destruction ofthe middle ear, with consequently impaired hearing, gradually leading tosevere hearing loss. These patients are normally helped initially bymeans of a tube through the tympanic membrane in a traditional manner,but the tube is expelled after a short time and the tympanic membranebecomes more and more damaged by these repeated treatments, and for thisreason the method does not help the patient in the long run. It wouldtherefore be desirable to devise a method by which it is possible toensure ventilation of the tympanic membrane in these patients too.

A standard procedure here is the restoration of the middle ear, whichinvolves removing excess connective tissue and enlarging the middle earby excising bone, primarily in the mastoid area. This surgery increasesthe chances of the patient acquiring better hearing, but it has to becombined with an air channel for successful results. The surgicalintervention is relatively extensive and cannot be repeated simply tomake a diagnosis of the condition of the middle ear. It would thereforebe desirable to have access to a channel which is large enough toaccommodate a fibre optic instrument for examining the condition of themiddle ear.

Where the normal method of ventilation via the tympanic membrane cannotbe used, other methods have been tried, among others ventilation linesthrough the Eustachian tube or ventilation tubes at the margin of thetympanic membrane, i.e. between bone and soft tissue. However, none ofthese methods has been successful and come into general use.

With the aim of reducing the risk of expulsion and thus avoidingrepeated surgical interventions, it is also already known to design theventilation tube in the tympanic membrane with an outer surface made oftitanium. The metal titanium has, as is known, been found to have uniqueproperties of biocompatability with the body tissues. Different areas ofclinical application have been tried out with success. Fixtures ofvarious types which are anchored in the bone are used to secure varioustypes of prostheses, for example dental prostheses in the jawbone of theoral cavity, and hearing aids anchored in the bone of the skull. In bothcases, the titanium surface adapts extremely well both to the bonetissue and also, respectively, to the mucous membrane of the oral cavityor the skin.

The metal titanium, with its excellent biocompatibility properties, hasalso been shown to have relatively high affinity for binding bloodproducts and forming tissue even on surfaces which are not primarily incontact with tissue. Among other things, this has led to ventilationtubes, placed in the tympanic membrane, becoming blocked more easily ifthey are made of titanium rather than of polymer material. In addition,a tube fitted in the tympanic membrane is in practice impossible toclean since the tympanic membrane is sensitive to contact.

Swedish Patent Application 8703694-3 describes a ventilation tube fortemporary healing into the tympanic membrane, which consists of aplastic tube whose outer side has been provided with a continuouscoating of titanium oxide. Alternatively, the ventilation tube canconsist of a titanium tube whose inner air channel has been treated witha layer which annuls titanium's normal affinity for body secretions andbody tissues, with the aim of preventing blockage of the ventilationchannel.

Although the described ventilation tube has advantages over conventionalventilation tubes made of titanium, this type of ventilation tube doesnot represent a solution in those cases where a permanent anchoring issought. In this case too, a certain amount of blockage of theventilation channel takes place sooner or later, and this makes cleaningnecessary.

Especially in the case of adults with chronic inflammation of the middleear, there is at the present time no satisfactory method for obtainingthe desired ventilation of the middle ear.

The aim of the present invention is to remedy the difficulties describedhereinabove and to create a permanent ventilation channel for the middleear.

According to the invention, this aim can be achieved by virtue of thefact that the ventilation tube is designed such that it can be anchoredin the bone tissue, for example in the mastoid bone. The ventilationtube therefore comprises, on the one hand, a front portion which isarranged to be introduced into the bone tissue and is designed so that apermanent anchoring of the ventilation tube is obtained, and, on theother hand, a rear portion which forms a passage through the skin. Inaddition, the ventilation channel is preferably designed in such a waythat blocking is minimized through both the design of the outer tube andthe choice of material for the inner channel of the ventilation tube.The ventilation channel is also designed in such a way that it ispossible to monitor the course of the disease in the middle ear usingfibre optics and in this way to improve the result of treatment.

According to one advantageous embodiment, the ventilation tube comprisesan outer tube which is made of tissue-compatible material with theability to grow firmly into the bone tissue and to function in theexternal and the internal epithelial passage. The ventilation tubefurther comprises an inner tube which is introduced into the outer tubeand which has the necessary properties for minimizing blockage. Thisinner tube is additionally releasable in order to permit cleaning orreplacement without causing damage to the supporting tissue. When theinner tube has been removed, a channel is obtained through theventilation tube which is large enough to allow the middle ear to beexamined by fibre optics.

According to a further embodiment, the inner tube is provided with amembrane so that the ventilation of gas (for example air, water vapour)can be permitted while, by contrast, liquid and particles/bacteria areprevented from entering. In this case too, the inner tube (the insert)is easy to replace.

According to a third embodiment, the outer tube is designed such thatits inner end is free in the excavated bone, for example the mastoidbone, and that it is surface-modified in order to make the ingrowth oftissue more difficult across the inner end of the tube. Suchsurface-coating can be obtained by known surface-coating methods, forexample by sputtering, and with known materials, for examplepolyurethane or silicon.

In all the embodiments, the outside of the outer tube is designed insuch a way that mechanical stability against the bone tissue is obtainedduring the healing phase, which is a precondition for osteointegration.

The invention is explained in greater detail hereinbelow, with referenceto the attached drawing which shows an example of an expedientembodiment according to the invention.

The ventilation tube consists of an outer tube 1 which is made oftitanium, and with the surface made of titanium oxide which is formedspontaneously on production. The outer tube comprises a front portion 2with an external thread 3 arranged to be introduced into a hole made inthe bone of the middle ear, so that the ventilation tube obtains a goodmechanical stability against the surrounding bone tissue during ahealing phase. This is a precondition for osteointegration and permanentanchoring of the ventilation tube. The threaded portion is designed atthe very front with cutting edges 4 in order to permit a certain degreeof self-tapping/scraping of bone material from the surrounding bonetissue when the tube is introduced into the pre-drilled hole in thebone, and cavities 4 a for accommodating bone shavings which have beenremoved.

The insertion end 5 of the front portion is unthreaded and has aslightly rounded edge towards the inner bore 14 in order to preventmaterial from being scraped loose from the inner tube 8 and ending up inthe middle ear when the inner tube is disengaged. After application,this unthreaded part extends a short distance into the middle ear andthis free end is therefore surface-coated with, for example, a polymermaterial for preventing overgrowth of tissue, for example polyurethaneor silicon.

The ventilation tube further comprises a rear portion 6 whose outersurface has a suitable shape for passing through the skin, and whichportion is of such a length that after anchoring of the ventilation tubein the bone tissue, it is arranged to extend from the bone/skininterface, through the skin and out into the open air.

Extending though the ventilation tube there is a continuous bore orchannel 7 in which an inner tube 8 made of polymer material, for examplepolyurethane or Teflon, is to be applied.

The opposite end 9 of the outer tube 1 is designed with an attachmentthread 10 for attachment of an assembly instrument for screwing theventilation tube into the bone. This attachment thread can additionallybe used for other purposes, such as the attachment of various inserts,for example filters, membranes or capillaries 11 of types known per se.It can additionally be used for attachment of an air pump (indicated bythe nipple 12 in the figure) for forced ventilation of the middle ear,should the need arise. Another area of application for the saidattachment thread 10 is to form an attachment for a plug, the insert 11being made solid. The bore 7 through the outer tube has such a diameterthat a fibre optic instrument can be introduced for examining the middleear.

The inner tube 8 has a length which is adapted to the length of theouter tube so that a certain free end is exposed in the middle ear whenthe inner tube has been pushed fully into the outer tube. The inner tubeis further provided with a flange 13 whose greatest diameter exceeds thediameter of the bore 7, so that the inner tube is prevented from comingtoo far into the middle ear. The inner tube can be easily replaced ortaken out for cleaning. Moreover, the diameter and length are chosen sothat liquid cannot readily pass through the inner channel 14 whenshowering and washing. Instead of the said separate filters, membranesor capillaries 11, these can, for example a membrane, be incorporated inthe inner tube. Such a membrane prevents water and bacteria fromentering and seals off from the outer tube.

The invention is not limited to the embodiment which has been shown byway of example, but can be modified within the scope of the attachedpatent claims.

What is claimed is:
 1. A ventilation tube comprising: an outer tube withexternal treads proximate to an internal end for anchoring into a boneof the ear; and an inner tube releasable with the outer tube and havinga through-channel for air communication between the cavity of the middleear and the outside air, wherein the inner tube includes a flange at oneend that prevents an opposite end of the inner tube from inadvertentlybeing pushed too far into the middle ear yet past the internal end ofthe outer tube.
 2. Device according to claim 1, wherein the inner tubeis a polymer material selected from polyurethane or polyfluroethylene.3. Device according to claim 1, wherein a front portion of the outertube is provided with an external thread and an unthreaded end portionthat provides a hollow extension from the external threads.
 4. Deviceaccording to claim 3, wherein, the end portion of the front portion issurface-coated with a material which prevents tissue from growing overit.
 5. Device according to claim 1, wherein a rear portion of the outertube is of sufficient length that after anchoring the outer tube in thebone tissue, it extends from the bone/skin interface, through the skin,and out to the open air.
 6. Device according to claim 1, wherein theinner tube has a length that extends the length of the outer tube. 7.Device according to claim 3, wherein an end of the outer tube oppositethe untreaded end portion is capable of receiving various insertsselected from the group consisting of filters, membranes, capillaries,air pump and plug.
 8. Device according to claim 3, wherein the innertube is capable of receiving inserts selected from the group consistingof filters, membranes, capillaries, air pump, and plug.
 9. Deviceaccording to claim 3, wherein the unthreaded end portion has a roundedshape and a gentle transition to the inner bore to prevent the innertube from being scraped against the edge of the opening and causing arisk of detached tissue material remaining in the middle ear when theinner tube is removed.
 10. Device according to claim 4, wherein the endportion is surface-coated with a polymeric material.